Designing a Phosphorus Removal Structure

Abstract

This chapter begins with a detailed presentation of the basic design methodology by estimating the mass of a specific PSM required for a specific site. This “design curve” will be thoroughly explained with several examples, as this is the heart of a proper design. Next, the reader is walked through the steps of a site assessment, with examples, that are necessary for obtaining all of the proper inputs for designing a PSM-specific and site-specific P removal structure. This includes how to estimate peak flow rates, average annual flow volume, typical dissolved P concentrations in runoff or subsurface drainage, and hydraulic head. Other inputs necessary for a proper design include the maximum area, or for ditch filters, the maximum length, the diameter of the drainage pipe to be used in the structure, the target retention time, maximum flow rate, and P removal and lifetime goals. Using all of the inputs, we present the general procedure for designing a site-specific P removal structure that meets the user constraints. This chapter also includes a detailed discussion on designing structures that flow from the top-downward vs. the bottom-upward, achieving proper drainage in a structure, and the challenges of balancing retention time with peak flow rate requirements. Although not necessary for design, we include instructions on how to predict the amount of particulate P that a P removal structure will remove. All necessary equations for obtaining necessary site inputs and conducting a design are given in this chapter.